The present invention relates generally to the field of wireless electronic communications. In particular, the present invention pertains to a specialized communication technique that supports reliable Asynchronous Transfer Mode (ATM) transmission of compressed video (e.g. MPEG video) on fading radio channels.
With the popularization of the Internet and the general increase in the technical sophistication of wireless electronic communication techniques, there has been an increased demand for efficient and reliable transmission of multimedia applications over wireless networks. Asynchronous Transfer Mode (ATM) is a known network communication protocol that provides for high speed switching and multiplexing of voice, video, data, and imagery regardless of the format. Application data is transmitted in short, fixed-size ATM cells comprising a five-byte header (40 bits) and a 48-byte payload (384 bits). The header conveys addressing information while the payload contains information bits that represent a segment of user data.
ATM is designed to facilitate high-speed transport of multimedia services in high quality commercial networks where communication channels have large bandwidths and low error rates. For wireless applications, though, link bandwidths are generally small and error rates large. The small bandwidth problem has generally been solved by using data compression techniques (such as MPEG video format) and/or by limiting the number of network users. However, a more fundamental problem with using ATM in connection with wireless communications has been that the quality of wireless links can be poor. Poor quality communication channels, referred to as xe2x80x9cnoisyxe2x80x9d or xe2x80x9cfadingxe2x80x9d channels, can result in unacceptable high levels of data transmission errors.
To monitor and correct for data transmission errors, one existing communication system applies error control codes to the headers and payloads of ATM cells. These error control codes are inserted into the headers and payloads of the ATM cells before transmission over the communication channel and are used by a receiving device to monitor the integrity of the data received and to correct transmission errors in the data. To assure a low cell loss rate, a very powerful code is used for the header, and to minimize the overhead associated with error control codes and achieve adequate throughput, a somewhat weaker code is used for the payload.
ATM transmission of compressed video poses different problems than transmission of voice, data, and imagery. To achieve a superior quality of service for MPEG transmissions, it is necessary to deliver a very small bit error rate (BER), on the order of 10xe2x88x926 to 10xe2x88x928, to the video decoder in the receiving device. This acceptable BER range is more stringent than that which is required for the effective transmission of voice, data, and imagery. If the delivered BER is larger than 10xe2x88x926, the degradation in picture quality can result in picture flashes, jumps, jerkiness, or even the entire picture going blank for a period of time. The necessarily low BER has been an impediment to the effective and efficient transmission of MPEG video over severely noisy or fading radio channels because such channels have very high inherent BERs and exhibit a mixture of independent and burst-error phenomena.
Ordinarily, to improve the performance of a coded communication system, the power of the error control codes are increased, thereby increasing the amount of coding overhead. While the additional overhead reduces the system throughput, the more powerful error control codes are better able to ensure the integrity of the data being transmitted. However, this approach is ineffective in connection with severely fading radio channels. Even when very powerful error control codes are used, severely fading channels still result in receipt of excessive uncorrectable error patterns, particularly because the transmission errors incurred over a severely fading channel typically occur in bursts and tend to be very concentrated. This is unacceptable when transmitting MPEG video because of the very low BER required to be delivered to the video decoder.
Accordingly, prior to this invention, the quality of MPEG video transmitted over fading radio channels was inferior. The present invention provides for a superior quality of service for MPEG video on severely fading radio channels.
The present invention comprises a system and communication technique for ATM transmission of compressed video (MPEG) that provides reliable data transmission over severely fading wireless networks. The invented system includes a transmitting device and a receiving device that communicate with each other via a wireless communication channel. The transmitting device includes a video encoder, an encapsulator circuit, a Bose-Chaudhuri-Hocquenghem (BCH) link coding circuit, a modulator, and a bit-by-bit interleaver circuit. The receiving device includes a video decoder, a decapsulator circuit, a BCH link decoding circuit, a demodulator and a bit-by-bit de-interleaver. The transmitting device transmits MPEG video data using ATM over the communication channel to the receiving device.
Prior to transmitting the MPEG data, the transmitting device applies binary BCH error control codes to each ATM data cell. Then, a predetermined number of ATM cells are interleaved. The interleaved cells are transmitted across the communication channel to the receiving device. The receiving device de-interleaves the ATM cells, detects and corrects transmission errors in the data, removes the binary BCH error control overhead and provides the error-corrected data to the video decoder to ultimately produce video on a display device. The technique of interleaving the ATM cells prior to transmission and de-interleaving the data after receipt essentially xe2x80x9cspreads outxe2x80x9d the transmission errors over many ATM cells instead of allowing them to be concentrated in a few ATM cells. The BCH codes are more effective at detecting and correcting errors in ATM cells if each cell contains a relatively small number of errors.